For a liquid crystal display device, since light from a light source for displaying images already has certain directivity while exiting the liquid crystal panel after being refracted and reflected, color distortion may occur when viewing beyond certain range of viewing angle. Therefore, viewing angle is an important parameter for evaluating performance of a liquid crystal display device. Viewing angle is the maximum angle at which a display can be viewed with acceptable visual performance. The viewing angle for a liquid crystal display device has two aspects, i.e., a horizontal viewing angle and a vertical viewing angle. A larger viewing angle means a larger displaying scope capable of being viewed with acceptable visual performance. The viewing angle for a traditional liquid crystal display device is typically 120°, which is always limiting the display performance of the liquid crystal display device.
In order to realize a wide visual angle display of a liquid crystal display device, IPS (In-Plane-Switching) technology has been proposed. The electrode structure in an existing IPS mode panel is shown in FIG. 1. In contrast to a liquid crystal panel wherein electrodes are arranged on both upper and bottom substrate at opposite sides of a liquid crystal layer, the most significant feature of an IPS mode panel lies in that pixel electrodes 3 and common electrodes 4 are both formed on the same surface of a bottom substrate 1 constituting a TFT (Thin Film Transistor) substrate, while no electrode is formed on the upper substrate 2 constituting a CF (Color Filter) substrate, However, since electrodes are arranged on the same plane, liquid crystal molecules are always parallel to the screen in any cases, which would reduce the aperture ratio and the light transmission efficiency. Therefore, when IPS is applied to large size liquid crystal display devices such as liquid crystal TVs, more backlights are required, which increases the structure complexity of backlight module and the cost of the liquid crystal display devices.